Methods for separating magnetic or magnetizable particles from liquids are employed inter alia in the case of continuous ore separation or in the case of water treatment. In this situation, the magnetizable particles may become magnetized during the process or may already be magnetized. The term magnetizable particles is also assumed to cover the term magnetic particles in the following. Magnetizable particles are for example magnetite (Fe3O4) particles obtained from iron ore bearing rocks.
Prefabricated magnetizable particles can also be used in order to obtain compounds from ores, for example by employing chemically functionalized or physically activated magnetized particles. With the aid of magnetizable particles, it is furthermore possible to separate trace elements from a solution, solids from a suspension, or liquids having different phases from one another.
Finely ground ores which are suspended with the aid of water can be used as solids. Constituents of the ores can then be bonded directly or after addition of the magnetizable particles, chemically or physically to the particles. Coulomb interactions for example can be used for physical bonds and sulfidic functionalizations can be employed for chemical bonds. The magnetizable particles “loaded” with the ore constituents or the magnetizable ore particles can be separated from the liquid by means of magnetic fields and processed further. In the case of “loaded” particles, the bonded ore constituent can subsequently be separated from the magnetic particles. The particles can be reused in the process.
With the aid of these methods, instead of solids it is also possible to separate liquids having different phases from one another, in water treatment for example. It is therefore possible for example to remove oils from water by chemically or physically bonding the oil compounds to the magnetizable particles. In similar fashion to the ores, the “loaded” magnetizable particles can be separated from the liquid. The particles can also be reused, as described previously.
A known system for separating magnetizable particles from a liquid, such as is known for example from WO 2010/031613 A1, is based on a tubular reactor having a traveling magnetic field. The traveling magnetic field is generated by electromagnets which are arranged along a longitudinal axis of the tubular reactor at the circumference of the reactor. The magnetic field generated by the electromagnets on the one hand provides for a movement of the magnetizable particles in the direction of the wall of the reactor. On the other hand, the traveling field provides for a movement of the magnetizable particles along the wall as far as a region of the reactor in which the magnetizable particles are extracted by suction from the reactor.
In order to be able to penetrate the liquid completely with the aid of the magnetic field and to be able to move all the magnetizable particles in the liquid in the direction of the wall of the reactor, the magnetic field generated by the electromagnets must be designed to be very strong. This equates to a high energy consumption by the electromagnets. In addition, strong magnetic fields can result in the magnetizable particles adhering strongly to the wall. A movement of the magnetizable particles along the wall may then require high magnetic field gradients which can vary in time, which in turn signify a high energy consumption by the electromagnets and a high level of technical complexity with regard to the design and control of the electromagnets.